Solvent treatment of naphthas and the like



tented ay '24, i938 UNITED STATES :.2,il18,77l SOLVENT TREATMENT or NAPn'rnAs PAEN No Drawing. Application May 15,, 11935,

' Serial No. 21,680

2 Claims.

This ihvention relates to, impi'bvements in the Edele'anu process for producing motor fuels, especially gasolines, of a high anti-knock value, described in United States Patents .No.' 5 1,585,473,1dated May 18, 1926, and No. 1,661,566,-

dated March 6, 1928, and also tothe production of improved lacquer solvents.

These patents describe processes of refining gasolines and kerosenes by splitting the crude distillate into a lower boiling and a higher boiling fraction, treating the latter with liquid sulphur dioxide and reblending the extract obtained by such treatment with the non-treated lighter fraction. This extract has a considerably higher content of aromatic andnnsaturated hydrocarbons than the original stock and, since the presence of these constituents in the motor fuel-is chiefly responsible for its anti-knock quality, it is apparent that by adding the extract obtained 0 from the higher' boiling fraction to the lower boiling one the anti-knock value of the latter is increased.

The anti-knock quality of a motor fuel is expressed by its octane number, the anti -knock value being higher the higher the octane number. By eniploying the processes described in the above cited patents it has been possible to produce gasolines havingoctanenumbers of. 70 to '75. Sulphur dioxide treatment of the higher 0 boiling fraction oi a gasoline. as described in said patents, has been customarily done at temperatures between +14 F. and +20 F., the extract obtained in this manner having an average concentration of aromatic and unsaturated con- 5 stituents of 351to 40 percent. a

New developments in the'design of internal combustion engines, especially for aeroplanes. make it desirable to refine the gasoline to such an extent that the octane number is raised above c the limit of 75 mentioned above.

We have found that such first grade gasolines may be produced by refining the higher boiling cut of the gasoline crude to such a degree that the extracts from this refining step have a very 5 high content of aromatic and unsaturated hydrocarbons and are largely free of saturated hy-' drocarbons. By blending such extracts with the untreated gasoline fraction of lower boiling range, a gasoline is obtained, the octane number 3 of whichmay be as high as 85 and above. With the methods employed for refining motor fuel so far, it has not been possible tocommercially produce such a gasoline. 4

For producing extracts of the specification given 5 above it is necessary to employ a solvent of excellent-selectivity. Unfortunately any solvent is only slightly selective on low boiling petroleum fractions such as gasoline. However, we have found that liquid sulphur dioxide exerts a very 1 high selective solvent action at temperatures sub- (oi. l96-37) stantially below 'zero degrees Fahrenheit, and

that, if'the extraction temperature is chosen sufiiciently low, the liquid sulphur dioxide splitsthe gasoline fraction into a raflinate being practically free of unsaturated hydrocarbons and an 5.

extract containing practically only unsaturated and aromatic hydrocarbons. v This split will be sharper and the more complete the lower the temperature of extraction, and there is no technical but only an economical limit to reducing the extraction temperatura- Two factors are of chief importance for fixing the temperature of treatment with liquid sulphur dioxide, the one being the boiling range of the gasoline out to be refiried and the other its original content of" aromatic and unsaturated hydrocarbons. The lower the boiling range of the gasoline fraction is and the higher its content of aromatic and unsaturated components the more advisablevwill it be to employ a'very low temperature in extracting. Temperatures as low'as -60 to -'70 F. are still allowable for technical reasons as well as'from an economical viewpoint. v I

According to our invention the following. dlf-. ferent steps may be employedfor producing an extract of the specification given above:

- (w) The naphtha fraction is treated with liquid sulphur dioxide at the conventional temperature of +14 to +20 F. in an extractiontower of con- '3 ventional. type. The extract layer obtained thereby by settling is further cooled down to about 60 to' -70 F., whereby this extract layer is again split in two phasespan upper rafllnate layer that has practically the samecharacter- 35 istics as the raflinate obtained in the first extraction step, and a new extract layer. which we may call second extract .and which contains in some inst tnces more than twice as much aromatic and unsaturated components as the extract ob- 40 tained in the first step of extraction.

(b) Refining of the naphtha fraction is done in one single step, whereby the naphtha is cooled down to -60 to -70 F. and continuously introduced into the base of a conventional extraction tower while liquid sulphur dioxide of substantially higher temperature, for instance it to 20 F., is charged to the upper part of the tower. In continuous operation a temperature gradient will result from this method, the temperature of the liquid gradually decreasing from'the top to thebase of the extraction tower. The extract withdrawn from the base of the tower'will be superior to that obtained in the first step oi the as method desbribed under (a),

(c) Refining of the naphtha fraction is done in a single step as described under (b), but bothstock and .liquid sulphur dioxide are charged to the extraction tower with a temperature of to to -70 F. The extract obtained in this way will have a concentration of unsaturated and aromatic hydrocarbons equal to or even surpassing that of the extract produced by method- (a), but requires somewhat more refrigeration.

In each of the three methods described above a series of mixers and settlers combined to make a unit that is conventionally called multi-stage mixing-settling equipment may be used in 'lieu of the vertical single extraction tower. It is further understood that the process described herein is not restricted to operation upon gasoline fuel nor to the temperatures specified above.

Both straight run and cracked naphtha can be treated in accordance with our invention to produce superior motor fuels; therefrom.

As illustrations of the improvement, which may be obtained in treating light oils at temperatures substantially below zero degrees Fahrenheit, we mention the following examples:

Example 1 A naphtha cut with 57.9 A. P. I. gravity and a. boiling range from 152 to 252 F. was treated in the countercurrent manner with 65% liquid S02 at +14 F. in one case and with 60% liquid- $02 at 22 F. in another case. The yields of raflinate and extracts and their specifications are The content of aromatic and unsaturated hydrocarbons was determined by means of sulphuric acid of 100% strength.

A comparison of the figures shows that the rafiinate yield is increased from 62% to by carrying out the extraction at 22 F. instead of at +14 F., and that the concentration of the arcmatic and unsaturated components in the extract was raised from 38.4% to 65%.

Example 2 A cracked naphtha with a 46.4 A. P. I., boiling range from 195 to 286 F. and containing as much as 50% aromatic and unsaturated hydrocarbons could not be extracted at all with liquid- S02 at +14 F. because of entire miscibility atthis temperature. However, by reducing the temperature to 22 F. a separation into raflinate and extract phase took place and the treatment could be carried out in the normal way. For comparison the cracked naphtha was treated with 100% S02 followed by two treatments with 50% S0: at 22 F. and in another case the same stock was similarly treatedat 60 F. The latter treatment resulted in a greatly improved rafilnate yield and in a higher concentration of aromatic and unsaturated components in the extract, indicating the advantage of extremely low treating temperatures in some instances. The

results may be seen in detail from the following table:

Radinate at 60 F. F.

Original Extract cracked nap h th a Extract at 22 F.

Yield percent by vol 100 19 81 40 60 A.P.I-.' 46.4 59.0 43.1 58.3

Percent aromatic and unsaturated hydrocarbons 50 6 61 0 80 Sayholt color +23 +25 Dark. +25 Dark.

The two fractions of the original naphtha from which the higher boiling one had been extracted with the result mentioned above had the following specifications:

Lower boiling fraction Boiling range 100-180" F. 0 Amount 93 vol. of original stock Higher boiling fraction Boiling range PTO-250 F. Amount 7 vol. of original stock The octane number of the untreated lower boiling fraction was '78.

The yield of extract from the higher boiling fraction was 60%, and this extract contained 80% aromatic and unsaturatedcompounds. The extract was reblended with the whole untreated lower boiling fraction with the result that the octane number was raised to 84.-

The extraction of naphtha fractions at such low temperatures as mentioned above can be avoided when using an auxiliary solvent, which increases the selectivity of liquid sulphur dioxide. In this case extraction temperatures as low as 14 F. are suificient to obtain extracts with higher 'contents of aromatic and unsaturated compounds.

I Example 3 The naphtha fraction used in this example had the following boiling range:

I. B. P. 220 10 229 20 232 30 236 40 240 50 244 60 249 "I0 255 80 263 276 End pt. 304

The A. P. I. gravity of this untreated fraction was 49.0.

This naphtha fraction was extracted with sulphur dioxide and several mixtures of the latter with an auxiliary solvent, such as ethylene glycol, diethylene glycol and trimethylene glycol. All extractions were carried out at 14 F. and the extracts showed the following specifications:

Extraction with sulphur dioxide plus ethylene glycol 20:80

Extraction with sulphur dioxide plus diethylene glycol 20:80

Extraction with sulphur dioxide plus trimethylone glycol 20:80

Extraction with sulphur dioxide A. P. I Percent aromatic unsaturated hydrocarbons 48 Saybolt color 60. 3 Dark ar a-771.

Other extractions were carried out with a similar favorable effect with mixtures of sulphur dioxide and the following auxiliary solvents: ben-' zy'lalcohol and diacetone alcohol. The separation of these auxiliary solvents from the railinates and extracts was effected with the first one by means of distillation and with the second one by means of washing out the solvent with water.

} As auxiliary solvents suitable for use in accordance with this invention, there can be used any solvent miscible with liquid sulphur dioxide andselective against saturated low boiling h-ydrocarbons, which has a suitable boiling point in comparison with the naphtha. fraction or which can be washed out of the raflinates and the extracts by means of other solvents easy to' separate from the naphtha hydrocarbons.

Naphtha extracts produced by means of liquid sulphur dioxide at the normally employed extraction temperatures of +14 to +20 degrees Fahrenheit have also been used as lacquer solvents. The kauri gum number is an indication of the amount of naphthenic constituents present in a lacquer solvent, and a good solvent should have a kauri gum number of not less than 70.

Example 4 tract determined.

Original (untreated) 4X37.5

Temperature, F Extract yield, vol- .ume percent Kauri gum Now..-

It can-be seen from the table that a satisfacmal extractions inasmuch as .they have a higher solubility for lacquer because of the higher percentage of aromatic and unsaturated components present. One of the great advantages of naphtha extracts over other lacquer solvents consists in that their boiling range increases gradually and (a) A naphtha sample was treated at F.

with 70% by volume S02. The extract solution, instead of charging it directly to the solvent recovery still, was first cooled to -60 F. which resulted in the separation of an intermediate oil. The three products, rafiinate, intermediate oil and extract, were freed from S02 and analyzed, the results being as shown in the table below. (b) The same naphtha was extracted countercurrently at a temperature decreasing from 0 F. to -60 F. ,with 70% by volume S02, the condi tions being such that the S02.was admitted at the top of the extraction tower at a temperature of 0 F. and the naphtha stock at the bottom at a temperature of .,60 F. By, suitable cooling arrangements the temperature at the top of the extraction tower was held at 0 F., in the middle of the tower at 30 F. and at the'bottom at 60 F. The results are shown in the table below.

(0) For purposes of comparison, the same stock was treated under the same conditions as-inf Treatment Or! a! 70 vol. percent 8011 at (5% 0 F. extract cooled to 70 m'ggg B0 I. to reject intero n; ,mediato oil Ref. 3 6' Extr. Ref. Extr. ml. in.

Yield 100 53.5 13.6 sac 66.0 34.0 sec M0 46.8 53.1 sec 34.0 54.0 33.6 53.0 m1 fines 29.8 2.0 9.5 sec 0.5 84.0 0m cat Kauri gum No 46.1 32.7 38.3 81.9 32.4 82.4 82.5 cm Octane No. r. n 51.9 Below 41 46.2 01.1 Below 41 90.6 Below 41 01.1

tory lacquer solvent cannot be obtained from a naphtha distillate with a naphthenic base by treatment at 14 F. (the usual treating temperature of solvent refining by the Edeleanu method).

- nor even at 0 F., but that it is possible to prolow +14 degrew Fahrenheit, that is down to 70 degrees Fahrenheit, are superior to the nor- It is evident from these data that the temperature gradient extraction, Example 5 (b) gives the same yields and qualities of rates and extracts as the normal treatment (Example 5 (0)). The extract obtained by rejection of the intermediate extract in Example 5 (a) has almost the same quality as the extracts obtained in Examples 5 (b) and 5 (c), but the yield is somewhat lower, the reason for this lower yield being that the intermediate oil which was obtained by cooling the original extract solution from zero to B0 F. still contains 1 amounts of aromatics and oleflnes. The intermediate oil may, of course, be recycled into the extraction tower, thereby raising the extract yield.

The invention is not restricted to motor fuels and lacquer solvents, but relates to the process of producing improved extracts and blends thereof suitable for these and other purposes; and where motor fuels and lacquer solvents are referred to in the claims, it is to be understood that we intend thereby to include any use to which the product is adapted.

What we claim is as follows:

1. A process for securing a high octane numtu ber motor fuel from a naphtha, comprising separating the naphtha into a low boiling fraction and a high boiling fraction, treating the high boiling fraction with liquid-S02 at about 14-20 F. to

produce a raflinate layer and an extract layer,

boiling fraction to a low temperature of the order of minus 60 to minus 70 F. and extracting in the countercurrent manner with liquid-SO: introduced at about 14-20 F., and blending the so-obtained extract with the low boiling fraction.

ERNEST TERRES. ERICH SAEGEBARTH. ,JOSEPH MOOS. 

